1. Field of the Inventive Concept
An apparatus and a method of the present general inventive concept relate to an image forming apparatus and a control method thereof, and more particularly, to an image forming apparatus and a control method thereof to improve quality of an image when a change in posture of a print media occurs.
2. Description of the Related Art
An image forming apparatus refers to an apparatus for forming an image corresponding to print data on print paper and encompasses a copy machine, a printer, a scanner, a facsimile, a multifunction copier with integrated functions of these machines, or other machines.
FIG. 1 shows a path of a print medium which is being conveyed according to a single-sided print mode in an electro-photographic image forming apparatus 1 employing an indirect electro-photographic system.
A print medium picked up by a pickup roller (not illustrated) is conveyed between a transferred unit 20 and a transferring unit 10 through a feed roller 2 and a registration roller 3. A visible image formed of a toner is formed on an image carrier 5. The transferred unit 20 includes an intermediate transfer belt 21, driving rollers 23, 24 and 25 for driving the intermediate transfer roller 21, and a transfer belt roller 22 for transferring the visible image of the image carrier 5 onto the intermediate transfer belt 21.
The visible image transferred onto the intermediate transfer belt 21 of the transferred unit 20 is transferred into the print medium passing between the transferred unit 20 and the transferring unit 10. In other words, when a voltage supplying unit (not illustrated) applies a transfer voltage having the opposite polarity to the toner to the transferring unit 10, a transfer electric field is produced between the transferred unit 20 and the transferring unit 10. The toner forming the visible image is transferred onto the print medium by this transfer electric field.
The visible image transferred onto the print medium is fixed on the print medium while passing through a fixing unit 13 and is discharged through discharge rollers 14 and 15 to the outside.
Here, while the print medium passes through the transferred unit 20 and the transferring unit 10, a posture, that is, an entrance angle, of the print medium may be changed. Such change of the entrance angle of the print medium may be caused by a variety of factors including a difference in rotation speed between multiple rollers arranged before and after pass of the print medium through the transferred unit 20 and the transferring unit 10, ambient environment conditions (temperature/humidity), thickness of the print medium, etc. When the entrance angle of the print medium is changed, a feature of transfer of the toner onto the print medium by the transfer electric field may be varied, which may result in an effect on print quality. Further, such change of the entrance angle may cause image defects such as variation of concentration of the image formed on the print medium, lack of toner in a portion of the image, etc.
FIG. 2 shows a double-sided print path of the image forming apparatus 1 of FIG. 1, in which the single-sided printed print medium is conveyed along a double-sided print path DP as the discharge roller 14 is reversely rotated. When the conveyed print medium again passes between the transferred unit 20 and the transferring unit 10 by means of a conveying roller 4 and the registration roller 3, a new visible image is formed on a rear side of the print medium.
Comparing the print paths of FIGS. 1 and 2, it is apparent that the double-sided print path DP is more curved than a single-sided print path SP. Accordingly, when the print medium conveyed along the double-sided print path passes through the transferred unit 20 and the transferring unit 10, a posture of the print medium may be changed in a pattern different from that in the single-sided print and an image defect or a change in concentration of an image may be caused in a manner different from that of the single-sided print.